The present invention relates to an angle detecting device which can perform an angle detection at high speed by using an absolute encoder and a surveying instrument provided with the angle detecting device.
A total station or a laser scanner is known as a surveying instrument, for instance. In the total station, a distance measuring light is projected to a measuring point, a distance measurement and an angle measurement are carried out on the measuring point, and three-dimensional data of the measuring point is acquired. Further, in the laser scanner, a pulsed light is projected as a distance measuring light, the laser scanner rotatably scans in a horizontal direction while rotatably scanning in a vertical direction at a constant speed, and three-dimensional point cloud data is acquired on a predetermined area or on an object to be measured.
Normally, an absolute encoder is used for the angle measurement (a measurement of a horizontal angle and a measurement of a vertical angle) in the total station. The absolute encoder has a pattern for an angle detection (a scale pattern), can measure an absolute angle, and is available at low cost. Further, although the absolute encoder can perform the angle measurement with high accuracy and with high reliability, the absolute encoder has such characteristics that a detection speed is low and is not used for a laser scanner which performs a measurement while rotating at high speed.
Further, normally, an incremental encoder is used for the laser scanner. The incremental encoder produces angle signals at an angle pitch as required, and an angle is detected by counting the angle signals. Although, the incremental encoder can perform the angle detection at high speed, a resolution of the angle signal itself is low, and it is necessary to increase the resolution by a signal processing.